A number of image forming apparatuses employing an electrophotographic method include photoconductive drums dedicated for yellow (Y), magenta (M), cyan (C), and black (K) and employ an intermediate transfer method for performing primary transfer of toner images formed on the photoconductive drums on an intermediate transfer belt, and thereafter, performing secondary transfer on a sheet using secondary transfer rollers. Such an image forming apparatus requires a long period of time from exposure to the secondary transfer by a distance from the photoconductive drums to the secondary transfer rollers since the secondary transfer is performed on a sheet after the primary transfer is performed on the intermediate transfer belt. Therefore, when an image forming operation is executed, the exposure may be started first before sheet feeding is started depending on a position of a cassette. Such an operation of starting an image forming operation before a sheet feeding operation is referred to as an “image-forming-first method”. On the other hand, an operation of starting the sheet feeding operation before the image forming operation is referred to as a “sheet-feeding-first method”.
Here, in a case where images are successively formed on a plurality of sheets, sheets may run out (paper out). In this case, the image forming apparatus has a function of continuously performing the image forming operation even after paper out occurs by automatically performing switching to another cassette accommodating the same type of sheets instead of stop of the image forming as a no-sheet error. This function is referred to as “auto cassette change (ACC)”. A method for performing switching of a cassette by the auto cassette change is disclosed in PTL 1.
In a case where the image forming apparatus which performs an image forming operation in the image-forming-first method performs the auto cassette change, image formation may have already been started when no sheet in a cassette is detected although depending on a timing when no sheet is detected. In this case, the general image forming apparatuses execute cleaning of toners which are formed on the photoconductive drums first and transferred on the intermediate transfer belt and execute image formation of the same page again after the cleaning.